This invention relates to heat transfer systems and has particular although not limited reference to problems of heat dissipation, especially in connection with electronics or like equipment. In use, some such equipment generates a heat flux of potentially self-destructive value. When a process of natural radiation will not reduce equipment temperature to an acceptable level, special provision for cooling must be made. Exposing the equipment to forced or natural air flows is one recourse, but in many instances this is inadequate, undesirable or impossible. Cold plates are known in the art, these being devices which provide a mount for heat producing components and further provide internal flow passages through which heat transport fluid circulates, absorbing heat by a conduction-convection process. Some ultimate heat sink must be provided, however, to accept the heat from the circulating transport fluid and here again heretofore known recourses may be inadequate, undesirable or impossible of use. For example, airborne electronics equipment may advantageously be housed in a closed compartment, as a pod on the exterior of the aircraft. Ambient surroundings in the compartment comprise an inadequate heat sink. Exterior heat exchangers, cooled by air flowing over the pod, are possible but are variabley effective according to the amounts and temperature of air available. In some situations air flowing over the skin of an aircraft is heated due to ram effects resulting from increased flight speed so that the circulated heat transfer fluid, instead of yielding up some of its heat to exterior air, would absorb additional heat therefrom.